Oxygen sensor deterioration-detecting device for internal combustion engines

Abstract

The air-furl ratio of an air-fuel mixture supplied to an internal combustion engine is controlled in response to an output from at least one oxygen sensor arranged in an exhaust passage for detecting concentration of oxygen present in exhaust gases. The deterioration of the at least one oxygen sensor is detected based on the output therefrom. When the engine is detected to be in a predetermined abnormal operating state, it is not permitted to monitor the output from the oxygen sensor for detecting deterioration thereof.

What is claimed is: 
     
       1. In an oxygen sensor deterioration-detecting device for an internal combustion engine having an exhaust passage, a catalytic converter arranged in said exhaust passage for purifying exhaust gases from said engine, an oxygen sensor arranged in said exhaust passage for detecting concentration of oxygen in said exhaust gases, and air-fuel ratio control means responsive to an output from said oxygen sensor for controlling the air-fuel ratio of an air-fuel mixture supplied to said engine, said oxygen sensor deterioration-detecting device including oxygen sensor deterioration-detecting means for detecting deterioration of said oxygen sensor based on an output from said oxygen sensor, the improvement comprising:   engine operating condition-detecting means for detecting operating conditions of said engine, said engine operating condition-detecting means including said oxygen sensor;   abnormal state-determining means for determining that said engine is in a predetermined abnormal operating state, based on an output from said engine operating condition-detecting means; and   deterioration detection-inhibiting means for inhibiting said oxygen sensor deterioration-detecting means from detecting said deterioration of said oxygen sensor when said predetermined abnormal operating state of said engine is detected.   
     
     
       2. An oxygen sensor deterioration-detecting device according to claim 1, wherein said abnormal state-determining means determines that said engine is in said predetermined abnormal operating state, at least when said output from said oxygen sensor falls outside a predetermined range. 
     
     
       3. An oxygen sensor deterioration-detecting device according to claim 1, wherein said engine is installed on a vehicle, said engine including an intake passage, said engine operating condition-detracting means including at least one of an engine coolant temperature sensor for detecting temperature of a coolant for said engine, an intake air temperature sensor for detecting temperature of intake air supplied to said engine, an intake pressure sensor for detecting pressure within said intake passage, an engine rotational speed sensor for detecting rotational speed of said engine, and a vehicle speed sensor for detecting traveling speed of said vehicle, said predetermined abnormal operating state of said engine including a state in which at least one of said sensors is abnormal. 
     
     
       4. An oxygen sensor deterioration-detecting device according to claim 3, wherein-said abnormal state-determining means determines that said engine is in said predetermined abnormal operating state when an output from at least one of said sensors falls outside a predetermined range. 
     
     
       5. An oxygen sensor deterioration-detecting device according to claim 1, wherein said engine includes an intake passage, a fuel tank, an evaporative emission control system for controlling emission of evaporative fuel generated from said fuel tank into atmosphere, said evaporative emission control system including said fuel tank as a component part thereof, an exhaust gas recirculation system for recirculating part of exhaust gases to said intake passage, said exhaust gas recirculating system controlling a flow rate of exhaust gases recirculated to said intake passage, a fuel supply system for supplying fuel to said engine, and an ignition system for igniting said air-fuel mixture, said predetermined abnormal operating state including a state in which at least one of said evaporative emission control system, said exhaust gas recirculation system, said fuel supply system, and said ignition system is abnormal. 
     
     
       6. An oxygen sensor deterioration-detecting device according to claim 5, wherein said engine operating condition-detecting means includes an internal pressure sensor for detecting pressure within said evaporative emission control system, said abnormal state-determining means determining based on an output from said internal pressure sensor whether or not said evaporative emission control system is abnormal. 
     
     
       7. An oxygen sensor deterioration-detecting device according to claim 5, wherein said exhaust gas recirculating system has a control valve for controlling said flow rate of exhaust gases recirculated to said intake passage, said engine operating condition-detecting means including a lift sensor for detecting a lift amount of said control valve of said exhaust gas recirculation system, said abnormal state-determining means determining based on said lift sensor whether or not said exhaust gas recirculation system is abnormal. 
     
     
       8. An oxygen sensor deterioration-detecting device according to claim 5, wherein said abnormal state-determining means determines that said engine is in said predetermined abnormal operating state, when an amount of fuel supplied to said engine by said fuel supply system cannot be controlled to a predetermined control range. 
     
     
       9. An oxygen sensor deterioration-detecting device according to claim 5, wherein said ignition system includes at least one spark plug, and at least one ignition coil for generating sparking voltage applied to said at least one sparking plug, said engine operating condition-detecting means including an engine rotational speed sensor for detecting a rotational speed of said engine and a sparking voltage sensor for detecting said sparking voltage applied to said spark plug, said abnormal state-determining means determining whether or not said ignition system is abnormal, based on an output from at least one of said sparking voltage sensor and an output from said engine rotational speed sensor. 
     
     
       10. An oxygen sensor deterioration-detecting device according to claim 9, wherein said abnormality of said ignition system includes a state in which a misfire occurs. 
     
     
       11. An oxygen sensor deterioration-detecting device according to claim 1, wherein said predetermined abnormal operating state of said-engine includes a state in which at least one of said catalytic converter and said evaporative emission control system is being checked for detection of abnormality thereof. 
     
     
       12. In an oxygen sensor deterioration-detecting device for an internal combustion engine having an exhaust passage, a catalytic converter arranged in said exhaust passage for purifying exhaust gases from said engine, a first oxygen sensor and a second oxygen sensor arranged in said exhaust passage at respective locations upstream and downstream of said catalytic converter for detecting concentration of oxygen in said exhaust gases, and air-fuel ratio control means responsive to outputs from said first oxygen sensor and said second oxygen sensor for controlling the air-fuel ratio of an air-fuel mixture supplied to said engine, said oxygen sensor deterioration-detecting device including oxygen sensor deterioration-detecting means for detecting deterioration of said first oxygen sensor based on an output from said first oxygen sensor, the improvement comprising:   engine operating condition-detecting means for detecting operating conditions of said engine, said engine operating condition-detecting means including said first oxygen sensor and said second oxygen sensor;   abnormal state-determining means for determining that said engine is in a predetermined abnormal operating state, based on an output from said engine operating condition-determining means; and   deterioration detection-inhibiting means for inhibiting said oxygen sensor deterioration-detecting means from detecting said deterioration of said first oxygen sensor when said predetermined abnormal operating state of said engine is detected.   
     
     
       13. An oxygen sensor deterioration detecting device according to claim 12, wherein said abnormal state-determining means determines that said engine is in said predetermined abnormal operating state, at least when said output from said first oxygen sensor falls outside a predetermined range. 
     
     
       14. An oxygen sensor deterioration-detecting device according to claim 12, wherein said engine is installed on a vehicle, said engine including an intake passage, said engine operating condition-detecting means including at least one of an engine coolant temperature sensor for detecting temperature of a coolant for said engine, an intake air temperature sensor for detecting temperature of intake air supplied to said engine, an intake pressure sensor for detecting pressure within said intake passage, an engine rotational speed sensor for detecting a rotational speed of said engine, and a vehicle speed sensor for detecting traveling speed of said vehicle, said predetermined abnormal operating state of said engine including a state in which at least one of said sensors is abnormal. 
     
     
       15. An oxygen sensor deterioration-detecting device according to claim 14, wherein said abnormal state-determining means determines that said engine is in said predetermined abnormal operating state when an output from at least one of said sensors falls outside a predetermined range. 
     
     
       16. An oxygen sensor deterioration-detecting device according to claim 12, wherein said engine includes an intake passage, a fuel tank, an evaporative emission control system for controlling emission of evaporative fuel generated from said fuel tank into atmosphere, said evaporative emission control system including said fuel tank as a component part thereof, an exhaust gas recirculation system for recirculating part of exhaust gases to said intake passage, said-exhaust gas recirculating system controlling a flow rate of exhaust gases recirculated to said intake passage, a fuel supply system for supplying fuel to said engine, and an ignition system for igniting said air-fuel mixture, said predetermined abnormal operating state including a state in which at least one of said evaporative emission control system, said exhaust gas recirculation system, said fuel supply system, and said ignition system is abnormal. 
     
     
       17. An oxygen sensor deterioration-detecting device according to claim 12, wherein said abnormal state-determining means determines that said engine is in said predetermined abnormal operating state, at least when an output from said second oxygen sensor fall outside a predetermined range. 
     
     
       18. An oxygen sensor deterioration-detecting device according to claim 16, wherein said engine operating condition-detecting means includes an internal pressure sensor for detecting pressure within said evaporative emission control system, said abnormal state-determining means determining based on an output from said internal pressure sensor whether or not said evaporative emission control system is abnormal. 
     
     
       19. An oxygen sensor deterioration-detecting device according to claim 16, wherein said exhaust gas recirculating system has a control valve for controlling said flow rate of exhaust gases recirculated to said intake passage, said engine operating condition-detecting means including a lift sensor for detecting a lift amount of said control valve of said exhaust gas recirculation system, said abnormal state-determining means determining based on said lift sensor whether or not said exhaust gas recirculation system is abnormal. 
     
     
       20. An oxygen sensor deterioration-detecting device according to claim 16, wherein said abnormal state-determining means determines that said engine is in said predetermined abnormal operating state, when an amount of fuel supplied to said engine by said fuel supply system cannot be controlled to a predetermined control range. 
     
     
       21. An oxygen sensor deterioration-detecting device according to claim 16, wherein said ignition system includes at least one spark plug, and at least one ignition coil for generating sparking voltage applied to said at least one sparking plug, said engine operating condition-detecting means including an engine rotational speed sensor for detecting a rotational speed of said engine and a sparking voltage sensor for detecting said sparking voltage applied to said spark plug, said abnormal state-determining means determining whether or not said ignition system is abnormal, based on an output from at least one of said sparking voltage sensor and an output from said engine rotational speed sensor. 
     
     
       22. An oxygen sensor deterioration-detecting device according to claim 21, wherein said abnormality of said ignition system includes a state in which a misfire occurs. 
     
     
       23. An oxygen sensor deterioration-detecting device according to claim 12, wherein said predetermined abnormal operating state of said engine includes a state in which at least one of said catalytic converter and said evaporative emission control system is being checked for detection of abnormality thereof.